New member, new PL400 owner

Insearchof

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#1
Hi All!

Been reading lots of threads on here lately and the vast amount of info shared by the members is impressive!
I recently acquired a 400 and knowing the limits of my talents decided to take it to get serviced and looked over before even powering it up.
The 400 looks nearly perfect on the outside but knowing the age of it, I exercised some self control and skipped firing it up and giving it a listen.
It's still being serviced/tested but a couple of quick questions I have:

Will or won't a fast blow inline fuse protect speakers if the amp suffers and dumps DC on the outputs?
The 400 manual I found says to fuse the speakers and some folks say it will save your speakers and others say don't bother as the speaker saved the fuse.
I'd like to hook up a pair of easy driving JBL 8 ohm vintage speakers and not worry that the woofer will be smoked. Replacement drivers aren't unobtainable but they aren't what I'd call cheap.
The typical fast blow fuses seems a little slow to react though. I've seen 200% ratings for 120 seconds. Maybe I'm wrong but that 2 minutes probably seems like a lifetime to a driver getting hit with DC.
I don't plan to push the amp/speakers hard so I'm thinking somewhere in the range of a 1.5-2 amp fuse for the content and output I'm looking for.
This pair won't see any 20hz bass drops either. I have other setups for that kind of music.

I found these faster acting fuses and wondered what the members here would have to say

http://www.littelfuse.com/~/media/e...ses/littelfuse_fuse_251_253_datasheet.pdf.pdf


Another question I had, How does a stock 400 (no upgrades) sound with modern pre amps? I have some vintage pre amps that I'd like to A/B compare on the 400 after they're serviced but for now it'll have to be modern stuff.

Long read, but I'd appreciate any thoughts.
 

Fishoz

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#2
Welcome Insearchof! You found the right place for answers.

Did you ever hear of a Flame Linear??....yes the PL400 reputation name given. DC protection cannot be resolved with a fuse. I was where you are in the beginning of my PL journey....must install DC protect! My PL400 was working just fine when I bought it a few years ago, found these guys here, luckily, before anything went poof (it took Lee to "poof" my 400). White Oaked it (thank you Lee) and now enjoying some very sweet sounds worry free (DC Protect has kicked in a few times...cooled her off and ready to go again).

Good luck on your journey with PL - it will be worth it!

BTW - I'm just a hack. I'm sure the guru's will be chiming in soon.
 

Insearchof

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#3
Welcome Insearchof! You found the right place for answers.

Did you ever hear of a Flame Linear??....yes the PL400 reputation name given. DC protection cannot be resolved with a fuse. I was where you are in the beginning of my PL journey....must install DC protect! My PL400 was working just fine when I bought it a few years ago, found these guys here, luckily, before anything went poof (it took Lee to "poof" my 400). White Oaked it (thank you Lee) and now enjoying some very sweet sounds worry free (DC Protect has kicked in a few times...cooled her off and ready to go again).

Good luck on your journey with PL - it will be worth it!

BTW - I'm just a hack. I'm sure the guru's will be chiming in soon.
Thanks Fishoz! I've been thinking that the DC relay will need to be added when funds and time will allow me to get the amp back to my repair guy.
I think perhaps my repair guy is somewhat reluctant to add anything on a direct coupled amp from maybe a SQ standpoint but I don't have anything else to compare it to. I've never heard a 400. Upgraded, output relayed or otherwise so it probably won't be an issue to me.
Sadly, I have heard the Flame Linear name thrown around on forums quite a bit. That's what got me started on this journey with my new to me 400.
 

laatsch55

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Halfbiass...Electron Herder and Backass Woof
#4
A stock 400 will have 40 year old outputs. Be gentle with them. When funds allow a DC protect board from member wattsabundant should be your first investment. A WOPL rebuild to full complementary output stage makes a world of difference in SQ...
 

MarkWComer

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Victim of the record bug since age five
#6
Don't even think of connecting your speakers without the DC protection circuit!

$99 compared to who-knows-how-much (and it can add up significantly!) for drivers and the time it takes to install them is well worth the money.

I have a 400/II and had a catastrophic transistor failure- half of the left channel outputs were straight conductors fro B-C, C-E, E-B- solidly FUSED! I'm pretty confident in saying that the DCP circuit prevented damage to the speakers (but only an alternate universe scenario could confirm that). The first two upgrades I did on that amp were the DCP and the control circuit, never even powered it up until those two upgrades were finished.

(Whoops- yeah, the capacitor upgrade, too...)
 

Insearchof

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#7
Once installed, Does the DC protection relay have any audible impact on the SQ?
I'm starting to think that the 400 should just go in the rack and look pretty until I get the wattsabundant board installed. Fusing the speakers seems to be ineffective.
The WO board kit looks really tempting but I'll have to keep that on the back burner for now.
 

oldphaser

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#8
Once installed, Does the DC protection relay have any audible impact on the SQ?
Without spending a lot of time on this, here are my musings on the subject......
(I also spoke to Lee yesterday about this.)

Relays may impact the damping factor due to the "initial contact resistance" of the points. However, how much damping factor is really needed for good audio has the been the subject of some debate. Suggested minimum damping factor numbers are in the range of 20 to 200:1. Phase Linear quoted 1000:1 (which is frequency dependent, i.e. @ 1000Hz or lower) on 400's and 700 series amplifiers with the exception of the Pro700 (which was 330:1)

NOTE: As an example; a damping ratio of 1000:1 would be an amplifier with an output impedance of .008 ohms into an 8 ohm load. 8/.008=1000

NOTE: I would also expect with usage over time, the contact resistance would go up.

According to the datasheets available on-line, the "initial contact resistance" of the following relays is:
1.) OEG PCLH-204D1S: 50 milliohms (at 1A 5VDC or 12VAC) Watts Abundant, Phase Linear 400's
2.) Potter & Brumfield T9AS5012-48: 75 milliohms (at DC6V 1A) Watts Abundant, Phase Linear 700's

The following were used by Phase Linear:
3.) Aromat HL2-P series: 50 milliohms (6V DC 1A) Phase Linear 300, A-15/30/60, DRS250/400/900 amplifiers *
4.) Arrow-M HG2-DC110V: 15 milliohms (6V DC 1A) Phase Linear D-500 amplifiers
5.) Guardian 900-A410-060713 (Unable to locate data sheet) Phase Linear 200 series amplifiers**


* The "damping factor" for Phase Linear 300, A-15/30/60, DRS250/400/900 amplifiers was 330:1 (at 1000Hz).

** The "damping ratio" for 200 series 1 amps was 100:1. The "damping factor" for 200 series II amplifiers was 1000:1.

I have to wonder how Phase Linear achieved 1000:1 on the D-500 and 200 series II amplifiers with a relay installed. None of the Phase Linear service manuals have you perform any damping factor tests. NOTE: The D-500 service manual has you bypassing the output relay for some tests.

Time permitting, I may start a new thread on the subject of relays.


Ed
 

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